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Thursday, December 11, 2008

Flocking of Birds is Commonplace in Winter by Ro Wauer

The adage “birds of a feather flock together” is a truism that has withstood the test of time. In South Texas, huge flocks of blackbirds are commonplace during late fall and all during the winter and early spring months. The flocks are most apparent during the evening and early morning hours when they move between their roosting sites and feeding grounds.

At least six bird species make up these huge blackbird flocks, and each flock often contains two or more species. Typically, flocks of red-winged blackbirds, brown-headed cowbirds, and common and great-tailed grackles are most common. And a flock of any of these may also contain a few of the others, as well as European starlings and occasional bronzed cowbirds. At times the larger flocks appear like wisps of smoke or clouds in the distance. These birds often fly together, only inches apart in a synchronously tight flock like they are in formation, wheeling, diving, and ascending as one. They eventually will descend as one to alight in a field or pasture to feed on available seeds and insects.

Although blackbirds are best know for flocking in huge numbers, many other birds also flock, especially during the non-nesting season. Geese, sandhill cranes, cattle egrets, quail, swallows, robins, and even wild turkeys and cardinals occur in single species flocks. And wintertime mixed flocks of songbirds can also be expected. This is especially true in the Tropics. In Manu National Park in Amazonian Peru, as many as 70 species have been found in a single flock. Closer to home, mixed flocks of five to a dozen species often can be found in the company of a few full-time resident species, such as titmice and chickadees.

One can’t help but wonder what advantage flocking might be for these birds. That question has interested ornithologists for a long time, and they have discovered a multitude of answers. Some are obvious. There undoubtedly is safety in numbers; at least one member of the flock is likely to detect a predator. It gives those feeding birds in the center of the flock more time to search for food and to eat in relative safety. New food sources can be found, for the good of the whole flock, when the individual isn’t spending the majority of its time watching for predators.

Other answers are less obvious. Flocks flying in close quarters seem to fend off diving hawks, as a raptor will not dive into a solid flock for fear of injury. Flying flocks will bunch up whenever a predator appears. In the case of a mixed flock, composed of species with slightly different feeding patterns, they also are more likely to discover a greater variety of foods. Those feeding in the canopy may frighten insects into flight that are then captured by a bird feeding at a different level. And also in mixed flocks, some species tend to act as sentinels, others as guides, and others as beaters and searchers.

It seems that our wintering birds, without the requirements of territorial defense, nesting, and feeding young, actually utilize a division of labor.